The present invention relates to a method and apparatus for controlling the temperature of components which are cooled by variable speed coolant flow. For example, in embodiments, the invention relates to methods and apparatus for controlling the temperature of components using the control of air provided by a variable speed fan, or a liquid coolant provided by a variable speed pump.
The primary fields of use for the present method and apparatus is in the control of the temperature of disk drives or storage media within data storage or test systems such as storage enclosures, racks or even test racks such as might be used during manufacture of disk drives or storage media. A test system would include a system for testing disk drives during manufacture. FIGS. 1A and 1B show schematic representation of examples of storage systems.
For brevity, the description from hereon will relate primarily to data storage systems, although it will be appreciated that the method and apparatus are equally applicable to test systems. Furthermore, as used herein, “storage system” is used in place of “data storage system”. Storage systems typically include plural storage media arranged somehow to enable data to be written to and read from individual media. The plural storage media are interconnected to storage interface modules to create a storage system. The media may be disk drives, solid state drives, or any other form of data storage medium. The storage interface modules may be interface switches, interface controllers, RAID controllers, processing modules or similar. The storage interface modules may be located remotely to the storage media, for example in the rear of an enclosure where the storage media are in the front of the enclosure, or co-located with the storage media, for example Interface switches (SAS Expanders) co-located with the disk drives in the front of an enclosure.
As the size and capacity of storage systems increases, there is an increasing need to provide efficient and effective means for temperature control and, in particular, cooling of the media such as disk drives within the storage system. Typically, a storage system includes storage modules which each contain plural disk drives and storage interface modules which provide internal and external connectivity between the storage media and the storage system external data fabric. It is known to pass cooling air through the storage system so as to remove heat produced in operation by the disk drives and thereby provide cooling to the storage system as a whole.
A typical example of prior art would use a ‘blade’ type structure. The ‘blade’ is high but narrow, allowing multiples to be fitted across the width of a rack, typically 10 or 12. Depth is determined by the number of drives being installed, but would typically be 3 drives deep and in to order of 500 mm. The structure of the blades limit the airflow across the installed devices and the density that can be achieved. Fully loaded blades can be heavy and this limits the maintenance and serviceability of the resultant system. Their weight also requires a structure across the width of the rack to support them.
FIG. 1A shows a schematic representation of such a blade storage system. As can be seen the storage system 1 comprises plural blades 3 arranged within the housing 5 of the storage system 1. Structure (not shown) across the width of the rack is provided to support the weight of the blades.
In contrast, a drawer-based system, as shown in FIG. 1B, uses a sliding drawer the full (or half) the width of the rack, but of low height. The height is governed by the storage media (or storage interface modules) installed, such that a single storage medium, e.g. an individual disk drive, is accessible and serviceable from the top of the drawer. The depth of the drawer is determined by the number of storage media installed, but is not limited in the same way as the blade. Since every storage media is individually serviceable the overall weight of the drawer does not become a serviceability limit. In contrast to the blade, the drawer is supported at its sides by the rack structure, relying on the strength of the drawer itself to provide support for the installed storage media.
One example of systems utilizing aspects of the invention comprises a rack into which are placed plural storage modules. Each of the storage modules contains two drawers which, in turn, each contain plural disk drives. At the rear of the storage system, storage interface modules provide control, input and output functionality. This is the means by which data may be written to or read from disk drives within the storage system.
Conventionally, one commonly used way to control the temperature of components in a storage system is with the use a “Proportional, Integral and Derivative” controller, commonly referred to as a PID or three term controller. A schematic example of a PID controller is shown in FIG. 2.
The PID controller 2 is arranged to receive as inputs an actual measured component temperature 4 and a set point value 6. Based on these inputs, an output signal 8 is generated representing a requested fan speed. In the example shown, the controller 2 is for use in controlling the speed of a cooling fan.
In accordance with PID control theory and as is well known, the output signal 8 is determined by three inputs 10, 12 and 14. The first input 10 is the “proportional” term and is based on the simple difference or “error” between the set point signal 6 and the actual measured component temperature 4. The second input signal 12 is produced by a differentiator 16 which is configured to receive the error signal and perform some further processing on it to derive the rate of change of the error signal. The third input signal 14 is a product of an integrator 18 which, again, is arranged to receive the error signal and further process it to derive a running sum of past error signal values. Each of the input signals 10, 12 and 14 is produced by the respective upstream component multiplied by a factor KP, KD and KI which is a constant. In a cooling control system, the output signal 8 may be used to drive a fan (not shown).
Thus, it can be seen that such a conventional PID controller functions in dependence on a difference between the actual and desired temperatures of the component as represented by the two input signals 4 and 6 it receives. In dependence on these, an output signal 8 is generated driving a new fan speed. By relying on continual adjustment of the fan speed the component temperature is accordingly controlled and brought towards the desired set point temperature.
PID controllers generally work well. They are particularly the best choice where there is an absence of knowledge of the underlying process. In the example given above, the underlying process can be thought of as being the flow of air past the component being cooled or temperature regulated. All the controller “knows” is that a certain fan speed is required, the knowledge being based on the measured temperature of the component and a set point temperature. Accordingly, with this limited knowledge there are situations where the control it provides will not be optimal.